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Chapter 4 General Switch Administration
SNMP Network Management Platforms
Using SNMP to Access MIB Variables
The switch MIB variables are accessible through SNMP, an application-layer protocol facilitating the
exchange of management information between network devices. The SNMP system consists of three
parts:
•
The SNMP manager, which resides on the network management system (NMS)
•
The SNMP agent, which resides on the switch
•
The MIBs that reside on the switch but that can be compiled with your network management
software
An example of an NMS is the CiscoWorks network management software. CiscoWorks2000 software
uses the switch MIB variables to set device variables and to poll devices on the network for specific
information. The results of a poll can be displayed as a graph and analyzed to troubleshoot
internetworking problems, increase network performance, verify the configuration of devices, monitor
traffic loads, and more.
As shown in
Figure 4-1
, the SNMP agent gathers data from the MIB, which is the repository for
information about device parameters and network data. The agent can send traps, or notification of
certain events, to the SNMP manager, which receives and processes the traps. Traps are messages
alerting the SNMP manager to a condition on the network such as improper user authentication, restarts,
link status (up or down), and so forth. In addition, the SNMP agent responds to MIB-related queries sent
by the SNMP manager in get-request, get-next-request, and set-request format.
The SNMP manager uses information in the MIB to perform the operations described in
Table 4-1
.
Figure 4-1
SNMP Network
Table 4-1
SNMP Operations
Operation
Description
get-request
Retrieves a value from a specific variable.
get-next-request
Retrieves a value from a variable within a table.
1
1.
With this operation, an SNMP manager does not need to know the exact variable name. A sequential search is performed to
find the needed variable from within a table.
get-bulk-request
2
2.
The get-bulk command only works with SNMP version 2.
Retrieves large blocks of data, such as multiple rows in a table, which would
otherwise require the transmission of many small blocks of data.
get-response
Replies to a get-request, get-next-request, and set-request sent by an NMS.
set-request
Stores a value in a specific variable.
trap
An unsolicited message sent by an SNMP agent to an SNMP manager indicating
that some event has occurred.
Get-request, Get-next-request,
Get-bulk, Set-request
Network device
Get-response, traps
S1203a
SNMP Manager
NMS
MIB
SNMP Agent
